Abstract The Ohio State University proposes to acquire a UHPLC-Trapped Ion Mobility (IM)-Quadrupole Time-of-Flight mass spectrometer to support the research efforts of NIH-funded users. The proposed instrument, the Bruker timsTOF Pro, was selected because it has several important performance characteristics that meet the challenges of major and minor users described in this application. These advantages expand the capabilities of users to perform clinical and biomedical research where sample amounts are very limited and characterize proteins that have isobaric peptide ?modforms? (distinct patterns of modification for a given peptide sequence). The instrument is unique in several respects: i) ?orthogonal? high resolution IM to achieve separation of coeluting peptide ions (e.g., isobaric peptide modforms), ii) significantly increased sensitivity (50-250 ng of proteins loaded for a typical LC gradient) due to tandem ion trapping with virtually 100% duty cycle, iii) high dynamic range that extends to over 4 orders of magnitude for ion detection, and iv) much faster analysis time (>100 Hz scan acquisition rate). Major users have performed comparisons between existing MS instruments in the core and the timsTOF Pro. For example, analysis of Human histone H4 modifications by major user Freitas yielded greater than twice as many isobaric peptide modforms from the N-terminal tail of H4 when using the timsTOF Pro as compared to the QExactive Plus. The timsTOF Pro also identified peptide sequences absent in the globular domain and C-terminal domain yielding 97% sequence coverage. Similarly, major user Hummon identified double the number of proteins (7,054 versus 3,038) from a mammalian cell lysate without significant benchtop fractionation, due to the ion mobility separation. These results, and several other similar comparisons described in the proposal, show that the timsTOF Pro will provide critically-needed protein identifications to NIH-funded research projects. The proposed instrument will be located in the OSU Mass Spectrometry and Proteomics Facility (MS&P) within the Campus Chemical Instrument Center (CCIC), a campus-wide Center that is administratively managed by the OSU Office of Research. The instrument will be operated by staff of the CCIC MS&P facility and highly trained experts from mass spectrometry labs of selected major-user research groups. The CCIC MS&P Facility is an established, well-utilized, university-wide core and the only proteomics core at OSU. It provides an optimum environment for a state-of-the-art instrument: a vigorous research community with great need for such an instrument and OSU faculty and staff with the expertise and enthusiasm to use the timsTOF Pro to its greatest potential. The requested instrument platform will be invaluable to a very broad constituency of researchers representing 8 NIH institutes.